Webbing…

Slackline is different from tightrope, tightwire, slackrope, (etc) in that it uses a dynamic webbing. Although slackline webbing feels flat, and feels static when in your hands, it is actually a tube (that is stretched flat), and once you put your weight on it you can feel it is quite elastic.

There is some semantic discussion amongst slackers nowadays as to what constitutes “slackline” as more and more longline walkers switch to stronger (less stretchy materials). If nothing else, slackline is 1″ nylon tubular webbing. It may include a couple other types of webbing too, depending on how you look at the situation.

The table below contains a bunch of common webbings (closer to the top) and then newer “exotic” webbings being used for longlines and highlines. If the strength rating has an asterisk (*) that denotes that I am providing an actual tested strength that is LOWER than the manufacturer’s rating (as I would rather provide the least optimistic number). A tilde (~) denotes I have approximated a value.

MIL SPEC vs CLIMB SPEC
If you look at the image above, you will see the tennis-ball-yellow (this color is called “citrine”) webbing has prominent horizontal ridges, like a backpack strap, and the red/silver/purple/orange webbings are smoother in their weave. The ridged weave is military spec webbing, the smooth weave is climbing spec webbing. For the most part, military spec is easier to find, and in a larger variety of colors. REI only carries climb spec in khaki and purple. Other colors can be found in climb spec, but usually have to be ordered through an Internet vendor (or maybe your local indie climbing shop has them). For the most part these webbings are identical. Climb spec is something like 6% stronger (19Kn vs 17.8Kn). I use both. Bluewater makes the climb spec webbing commonly found (sometimes Sterling climb spec can also be found, and sterling has a special climb spec version that I have yet to try, called “tech tape” which will hold 20Kn).

9/16″ AND 11/16″
There are tubular webbings available in smaller sizes than 1″ — both 9/16 and 11/16 inch webbings are available, with 9/16 usually being easier to find (also called half-inch sometimes). 11/16 = 13.3Kn (3000lbs). 9/16=9Kn (2023lbs). Either of these webbings will probably hurt if you walk them barefooted, but in shoes they feel fine, and in general they stretch more than 1″, accentuating the “bounciness” of the slackline. I like to walk half inch because it’s fun for bounce and surf tricks, and it looks more like a “wire” to observers who don’t know what slackline is.
2″
Two inch tubular webbing is super strong (30Kn!), but doesn’t wrap well around carabiners because of its width (forget about primitive tightening, it won’t slip through the ‘biners), and it stretches very little. It’s great for jump lines, assuming you can pull it tight enough (ratchet, pullies, etc). Some specialized jump lines (like those from Gibbon) are not nylon tubular 2″ at all, but a flat polyester or similar.

THREADED LINES
One way of strengthening a line is to run a smaller line inside of it. In the image above you can see the red 9/16″ has been threaded inside of the silver 1″. The physics of this are still up for debate — certainly the two strengths are not just added together (!), but anecdotal evidence and pull tests show that threaded lines are stronger. As half inch is stretchier, there have been instances where the outer line breaks and the inner holds. Also, if the outer line frays, the inner will become visible, which can be a nice safety. Of course, threaded lines weigh about 50% more.

TYPE18
This is a flat (non-tubular) type of military webbing that is no longer made, but still available from some retailers. It’s approx 50% “thicker” than tubular 1″ but has the same 1″ width. You can see it compared to mil-spec 1″ here and here. It weighs double that of tubular one inch, and offers a 6000lb (26.7Kn) break strength. Line locker pull tests done by others have shown it to break around 7200lbs, so it’s likely the 6000lbs is underrated. It stretches about half as much (9-10%) as tubular 1″ too, so keep that in mind. For normal walking it feels great, very supple, but for jumps and whatnot it is noticeably more ‘static.’ This webbing works great for highlines, but beware of barehanded catches, it is known for bloody palms. A word of warning: Type18 can be somewhat hard to find, is not cheap, and there are some retailers selling “knockoff” versions. I buy mine directly from Yates.

Be aware, the info below applies to people who are rigging 100+ft lines. On a short (30-60ft) line, any method is fine!

KNOTS
You’ll find there are several different ways to affix a line to another line, or a line to a carabiner. The most basic is a knot, usually a waterknot. A waterknot is just an overhand knot tied in two pieces of webbing, and they backtrace each other. The larger the bend-radius of a knot, the stronger it is, so I sometimes insert a third 10″ piece of webbing to act as “filler.” (see this pic for example) Knots generally reduce line-strength to about 50-65% of rated. If the line is tied in a loop (a “basket” configuration), the strength of the line is doubled, so overall you can expect at least 130% or so of the regular line’s rated strength.

LOCKERS
Line lockers are great — I swear by them. They generally do not reduce the strength of the line significantly, so just make sure you use nice, fat, solid lockers. That being said, it is possible to break/bend lockers. I use a lot of steel rap rings as lockers, many of which I’ve sourced from one vendor. These are supposed to be 10,000lbs break strength, yet loading a line with way less than 2000lbs of load, I was able to bend one of these rings close to failure; so watch your gear, double up for protection if possible, use backups, and tie things off so they can’t go flying. If you want to know more about line lockers (how to use them, which to buy, etc) … see this post.

STITCHING
A bartack is a type of burly industrial stitching used to fuse webbing to itself (or to other webbing). Each bartack can hold around 700lbs, in nylon webbing, meaning that a series of ten should be stronger than the webbing itself. I used to trust stitching more than any other solution, but recently I had a couple of bartacked lines nearly fail on me, and I have stopped trusting stitching that hasn’t been done (and tested) by large companies. I would still trust Petzl (etc) slings, as I know these companies randomly pull-test their products to ensure safety, but I am no longer trusting anything I’ve had custom made by small vendors. The stitching in question began to pull out at around 1500lbs of load. This is highly unsafe.

Just how much tension can you put in a slackline?
In the first of our tests, here’s adam putting 332lbs into a line barehanded, then ~450lbs with a carabiner for a handle, then almost 800lbs with two pulleys and some cord.

7 Comments

Hello Adam,
First of all, Thanks a lot for your great work and sharing.
I am living in Turkey and I dont have too many options for webbings to buy. Now i could find the white one of this webbing at my local store “edelrid 25 mm x-tube” (http://www.edelrid.de/en/sports/products/slings/25-mm-x-tube.html) but i could not find an information about the elasticity of the webbing. it says on the web site, this is perfectly suitable for the slackline but i want to buy about 250 feet for the longlines and highlines. Do you have any information about the streching percentage of this webbing or have you ever tried this?
Thanks

REPLY: Hi. The page you linked said it’s 43 grams per meter. Normal slackline webbing is 40 or 41 g/m, so that sounds like normal webbing to me. Also, the site you linked said 20KN strength, which is close to normal webbing.

I like the look of this webbing, especially the “oasis-night” color. Anyway, it looks like normal nylon webbing to me, based on the ratings, albeit a different brand/color than I have ever seen. If I had to guess, I would say the typical max 20% stretch that nylon webbing has (before breaking) would be the same here. I do not believe this is polyester webbing (which stretches less). If you have any doubts, maybe buy a small piece and do some testing. Or if you want to mail me a one or two meter length I can break test it for you with a line locker to verify its strength (poly webbings break at very low numbers in line lockers or when knotted, so you must always use a zilla or banana or awl with them). If you can also buy the “supertape 16mm” you could thread that inside the 25mm webbing for a stronger line. I would be careful highlining on any webbing you do not know the characteristics of the line (e.g. nylon, poly) and what rigging equipment will work best with it.

Also, as general highlining advice, don’t ever highline on a single line (always at least one backup); most people today are using stronger materials than normal tubular webbing. In years past doubled up tubular webbing (perhaps with a climbing rope beneath) was considered safe. Now in a quest for safer and lighter many people are moving to newer webbing types; Type18, vectran, Gibbon Proline, etc. I know of people who have highlined on single tubular with two thinner (15mm) lines threaded inside it, and that is another “reasonably safe” option.

A 200-250ft piece should make a good longline, especially if you thread another line inside it. Looking on google at other places where people have reviewed it, it seems like normal climbing nylon webbing.

curious about the lower than rated breaking strengths for white magic and slackstar distance. i am not used to hearing about slackline gear having optimistic ratings, i was under the impression that all companies saw the value of being conservative. also your 25kn for white magic is really really low compared to their 33kn and 30kn 3 sigma ratings. can you share some info about your tests and how they failed so low?

thanks!

EDIT FROM ADAM: these were Terry’s tests, and this was years ago before we all knew about the need for large rollers with poly webbings. I am going to re-do this article for the longline webbing video and put in the correct numbers then.

EDIT: it is basically the same as Sterling TechTape, except for two features (one i love and one I think is sort of marketing). 1: it is available in extreme lengths, whereas TechTape maxes out at 300ft (maybe a bit longer if you get lucky when you buy a whole roll). Sterling will sell you a roll with “no splices” specified, but 300 is the max. BC’s stuff can be way longer (I have a 400ft piece that we stretched to 458′ and I walked in 2012) but of course with such a low break strength compared to newer webbings I would not plan on walking 400+ft unless you like very loose lines. I walked the 458 on my second or third try so I do now wish I’d bought a 600′ piece instead haha. 2: It has the tracer stitching integrated into the weave so it’s the “smoothest possible” feel on the feet. I walk in shoes so this doesn’t affect me and even barefoot I feel it would be a “princess and the pea” situation to actually detect tracer stitching with your feet. Both SlackSpec and TechTape being nylon climb-spec weave are some of the softest webbings you can buy, there literally hasn’t been a single time I have coiled either of these webbings up and not inadvertently thought “man this feels so nice in my hand”. Compared to the feel of Mantra or TubeLine etc they are basically velvet haha. As for downsides: only available in red, and the price might be a bit above Sterling. But you also “support the community” which is pretty cool. I think that does it. I will do a review on this webbing soon (I’d like to do reviews right when stuff comes out, but I’d feel weird not using it for a year or two so that I can speak from experience).

As I drooled over the gear and great production of your guide to longlining I noticed something that immediately made my dirt bag climber ego rear its long main of greasy, unwashed, matted hair (metaphorically of coarse). It was your homemade sling in the webbing anchor installment. It looked to simply be a section of climb-spec webbing sewn together (orange with white stitching on the end of your webbing anchor). I was wondering… One. Do you consider those as strong as other nylon slings? Two. What type of thread did you use to sewn it? I see myself possible replacing the water knotted slings I carry my draws with (maybe some draws too), and the slings to wrap trees for slacklining with stitched ones. Maybe I could find this info else where on the interweb, but your intelligent, thorough, and SAFE endorsements of specific products leaves on feeling reassured and confident in their purchase, creation, and use of life preserving gear. Thanks for your awesomeness! Happy balancing.

Humble follower

John

EDIT: The sling you mention is actually made by Bluewater, at least if I am thinking of the right one. To confirm, you mean this one, right?

Anyway, if that’s the one, that is a bartacked sling from Bluewater. It’s rated for 7200lbs. Each bar tack is usually good for 500-1000lbs depending on the thread type and the number of stitches per bar (usually between 23 and 42 I think). You “can” sewn your own slings this way, but I don’t recommend it as the type of thread, quality of sewing, etc, makes a huge difference in it breaking or not. So either find pre-sewn slings in the right length, or second best is find an FAA certified master rigger (look for your local drop zone where folks skydive) and pay them to do it, since they are specifically trained to do ad-hoc repairs and joins of exactly this type of material for these same sorts of stresses. I do have a friend who sews his own and I tested some single bar tacks recently to see what they would hold, but again I need to stress that it depends a lot on skill and thread type. In his case the tacks blew out at about 250lbs (and he is just finishing a flavor of industrial design degree where he does a ton of hands-on stuff and has been sewing his own anchor slings for years), so this sort of confirms that it would be better to have it done by a bartacking machine or by a pro-rigger, since there is zero chance someone like me (minimal sewing skills) could even reach his level, let alone that of an FAA master rigger.

Hi Adam, I have absorbed at as much info as possible on your website as I can when it comes to buying what I need but if i’m honest i’m not a very savvy consumer and was just wondering if I could get some advice from yourself.

I’m going hitchhiking around New Zealand in a few months and want to take a slackline with me. I was wondering what the best webbing/lock rings/caribiners to purchase would be. Bearing in mind I need to save weight.
I’ve watched your HOWTO video on Youtube setting up a primitive system and I figure I need 4 caribiners, 2 lock rings, 2 slings and webbing.

I usually slack on a 25m Gibbon classic and have little experience of 1″
webbing however I have tried it and I does feel nice on the feet. I want to be able to rig a 15m-20m line on my travels but don’t know how much webbing will be needed as you’ve got all that to and fro between caribiners at one end.

Sorry if I’m waffling away on your website lol. If you could get back to me it would be massively appreciated dude. Peace x

EDIT: I think I’m going to do an article about this soon actually. For now, let’s say 4 oval ‘biners, 2 forged rappel rings, 2 slings that will be likely to wrap the trees in the area you are headed, and enough webbing to stretch that gap you want to walk plus another 30-40% of that length. So if you want to walk 20M, you’ll want to get 28M of webbing. Except if you’re planning on rigging a line longer than about 13M or so (~40ft) I would consider also doing the “strength of three men” method. If budget or weight is a major concern you can substitute the two pulleys and cord for two carabiners and just a bit of extra length in your webbing (add another 10%) and just use girth hitches to attach the carabiners (and use them like pulleys). If this doesn’t make sense, e-mail me. I will do an article soon that covers how to do this.